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Choosing thickness

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I've read lots and looked at lots of DVD's and videos and can't recall anyone commenting on how to decide how thick to make a bowl. Would the experienced turners comment on what considerations go into deciding this?

Thanks.

Dean Center
 
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What's it for?

If you're just going to look at it, pick what pleases you, or try to pick something that pleases critics. There's a sort of fetish about thin walls among some turners, but though they might be nice for piercing, they won't take a lot of carving. Thin stuff usually fails the drop test first time.

If you intend the bowl to be used, you want to go a bit thicker. I end up around 3/8 on a 16", and they've survived drop tests, even on endgrain. Quarter begins to push the drop limit.

After that, go with thicker bottoms for popcorn bowls, where you don't want to get a lap burned. I like a grip ring design for something to be passed about, but not for a salad bowl where people toss toward center. Heavier center weight there. Don't bother about the myth that walls should be of uniform thickness. You're not putting clay into a kiln, you're putting wood on a table. Make it look good, even if it will serve as well.
 

john lucas

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Most bowls I make as user bowls are about 3/8" to 1/2" thick. If it's small bowl under 6" they probably stay on the 3/8" or thinner range. If they are truely functional I try to make them feel substantial enough to take abuse. Now how thick that is I don't know. On a 12" bowl around 1/2" thick for that kind of bowl. My non user bowls are usually quite thin, 1/4" or less. It just a personal thing, no particular reason.
 
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Most of mine are in the 1/4 to 3/8 inch thickness range. I turn green to final thickness, and then dry, and if I leave them much more than that thickness, they tend to crack more, and take longer to dry. I turn a consistent thickness for the whole bowl wall, and bottom. Some like a heavier rim with a slight under cut to make it easier to grip, which makes no sense to me. I was a bowl last weekend at a show that is intended for serving Kava (not really sure what it is, but a plant/brew/tea that is good for you) and it was over 1 inch thick for wall thickness, and the base was maybe 3 inches thick, and total height was 16 inches. Really too heavy for my taste, but fine for its intended use. They do have to 'feel' right. Some that are thick but feel too light don't sell. Ones that are too thin don't sell except to the art crowd.

robo hippy
 
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Another consideration I didn't see mentioned above is the type of wood. Some are quite elastic where others are brittle, and still others are stable while some move drastically. These factors combined with the intended use of the bowl will determine the appropriate thickness. These numerous variables are determined to some extent though practice/experience. If you were turning apple, a thick bowl would likely crack, and a very thin bowl would likely distort drastically (as one obvious example). While a thin bowl of boxelder would be somewhat brittle, but so light its ablity to survive a drop would probably be determined far more by its shape and grain orientation which is yet another variable.

I do have to disagree at least in part with the idea that thin bowls will not survive the "drop test" by virtue of the fact that they are thin. This again is based to some degree on the shape, overall diameter, grain orientation, and type of wood. Vessels made of some woods are drastically lighter and due to their thinness are more flexible, both of which can preserve them when dropped. And although I do alot of thin walled turning, it isn't done just for the sake of turning thin, fine piercing work with an NSK requires 1/16 or thinner with most woods so its a function of the design.

I don't have MM's years of experience, but I have never had a bowl break from dropping it (although I don't honestly make a practice of it). And as I learned from Steve Sinner, a sudden flair in or out at the top of an open vessel can add tremendous strength to a thin object (which can be seen on his pierced cylinders. I have turned lap shades with a slight flair that are 1mm or thinner and they would and have easily survived being dropped.

So the answer to your question is that there are many variables to consider, but you first must start the design based on the intended end use. Whether it is a sculpture or a popcorn bowl, form usually follows function.
 
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Thinking back on thin bowls, I have had some very thin pieces that when dropped (blown off shelves at shows), they had almost no damage. So light (lite?) they bounced and showed almost no abrasions from landing on concrete.

Different woods do better with different thicknesses, but the drying is as much of an art as the turning, and shaping of the bowls. No one size fits all here.

robo hippy
 

john lucas

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I remember many years ago they had a show in our gallery. The guy called them potato chip bowls. They were bowls or maybe somewhere between bowl and platter that were extremely thin. Usually made out of crotch wood or other figured wood. They were very warped. Not a single one of them sold. I always wondered why. They obviously weren't functional but were very well done and had some great figure in the wood. Did people not like them? Did they think they were too fragile? Was it a crowd that thinks wood should be functional? I never did find out but always keep that in the back of my mind when I make something thin.
 
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John,

It may have had to do with how they were presented? If they were simply presented as a novelty, not likely anyone would have paid the typical price of a fine turning. Those "potato chip" vessels have been an influence even if not through sales. I have seen others do them in response to that set and gave them the same name.

The only time I have seen thickness impact buying/selling is when the item was poorly done and too thick. For thin walled items that sell, consider Binh Pho, probably one of the most collectible turners around. He jokes that the more useless a piece of wood, the more $ you can ask for it.
 
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Years and years ago I ran afoul of our dean of the school of art and design. She was giving a workshop on how to enter juried shows. I had an endgrain black ash bowl about 10" across and 1/4" thick rim to near bottom for show and tell. Problems with the piece were that "I've seen a lot that were turned thinner" and "you have two features competing for attention." Branch and heart were the two features. All survived ON AN ENDGRAIN turning!

I couldn't take away much from any piece of wood, but every year for local shows I turned a thin piece or two in honor (spite?) of her. Had to weight them to keep them from becoming airborne, as some made ideal airfoils. Some I've made have pleased even SWMBO, but most would, I am certain have been as well-received if they were thicker. Except by Diane. I use them to hold my business cards and the lexan weight that holds them down. This little ~7" piece sold in the first five minutes of a two-day show, so I had to put the cards in another bowl. http://i35.photobucket.com/albums/d160/GoodOnesGone/Weirdo.jpg

http://i35.photobucket.com/albums/d160/GoodOnesGone/Cherry-Top.jpg
 
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Dean, here in Hawaii jack Straka and Dan Deluz for whatever reason aimed at around 3/16 wall thickness. That became a standard. Monkey see thing. That said. With many years as a production turner a 12 in or less wide bowl around 1/4 in thick. Heavier or not in the bottom. Traditional Calabash bowls were made thicker in the bottom as they had a round bottom. My translucent work is around 1/8th thick. Large salad bowls 5/16 maybe more. Bowls with great spalting sometimes looks great with a wide rim to show off the spalting. Does not bother me in the least to give a bowl a 1/2 wall thickness now and again. Some folks really like thicker work. A rocking bowl can be very thick with a really wide rim and a very small bowl in the center. For super grained pieces of wood or as a canvas for coloring etc. In my use and care brochure I say last but not least. If you drop a bowl expect it to break. Most functional bowls tend to do fine though unless they land on a rim. Carpet is one thing wood and stone another. I mostly get my thin translucent work back for repair. Anything from a cat, wind, person cleaning and knocking the piece to the floor or God. Folks that challenge me about breakage saying it just happened. Thin work always has help in breaking. Whether the owners know about it or not. I got a salad bowl back a few months ago. Two splits on each end grain side. I determined it was my fault. I had not seen the natural hairlines coming from tree center and they became visible with time. I put in a butterfly patch on each line. cleaned and refinished the work. Picked up all shipping and sent it back to them. If the bowl had been 1/2 thick or the 1/4 it was, the lines would have shown up. My advise is to make a number of pieces with varied thicknesses and see what works best for you. A thick bowl is easier to do. Sign and put the year you made it on the bottom. I just repaired a translucent work with a hairline crack. I did not have to guess when I turned the work upside down. It said, Kelly Dunn Norfolk Pine 1998. The owners had no problem finding me. I sign my name so it can be read. Not my check signiture. Be proud of what you make and expect to grow in your talent as time goes by. You will know what I mean when you see a piece you did twenty years ago. collectors sometimes want to cronicle a makers growth and will seek out examples of various time frames. I hear from collectors now and again who tell me they own my work from when I went full time in 89 and add a piece now and again. Now that makes me feel good. It will you also.
 
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How thick I make a bowl is usually a function of how deep my last catch was.

Having said that, I aim for 1/4" for about 6" and smaller and 3/8" for larger bowls or ones that will see frequent use.

Dean: After reading the replies to your post, have you made up your mind on how thick to make a bowl?


GK
 
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Greg,
I think I have. Most of my woodturning is 'accidental'--like your comment about your last catch. I aspire to one day being an 'intentional' turner. As I work toward that, I'm going to make the thickness what seems right to me for the particular wood and design I'm making. Or what's left after the 80 grit gouge.

Dean
 
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I would also suggest a practice exercise of turning as uniformly thin as you can. Not for the sake of turning thin, but because it facilitates a great learning process. It is a good exercise in tool control, improving cut quality, avoiding chatter etc and a learning process about how the wood reacts as it become increasingly thin. You will find as you get very very thin you simply cannot proceed with poor quality cuts, the wood will resist and let you know that you are not cutting properly. This feedback from the wood is not nearly as apparent with a solid thick piece of wood. It will help you to break any habits of forcing a poor tool presentation/cutting angle etc because it provides instant feedback from the wood and helps you to learn to turn based on sound and feel. Doing this exercise 4-5 times probably taught me more about making a good cut than reading 4-5 books on the subject.
 
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